Abstract : This report provides details on two tests performed to determine if 1.5 Index of Refraction (IOR) glass beads are suitable retroreflective material for USA airfield markings. The tests were done at Ellsworth AFB SD from 25 Sep 91 through 9 Jun 92 and at Tyndall AFB FL from 12 Dec 93 through 24 March 95. During the first phase of the project, two taxiway centerline stripes, separated by a six-inch gap were applied on the primary aircraft taxi route at Ellsworth AFB SD. Each was reflectorized with glass beads applied at approximately the same rate, but one was reflectorized using Federal Specification TT-B-l325B, Type 1(1.5 IOR) beads and the other with Type III(1.9 IOR) beads. The test stripes were evaluated by 91 pilots and civil engineer personnel for approximately nine months through visual comparison and measurement of the retroreflective intensities of the two lines. The empirical data demonstrates the 1.5 IOR beads were more durable than were the 1.9 IOR beads. The pilots' evaluations showed that 1.5 IOR beads are suitable for airfield apron and taxiway markings. During the second phase of the project, the primary runway at Tyndall AFB FL was marked, again using the two different types of glass beads; however, these were procured under Federal Specification TT-B-1325C, an updated version modified to improve the performance of the Type III beads. The pavement markings applied on the north side of the runway centerline were reflectorized with Type I glass beads, and Type III glass beads were used 10 reflectorize the markings on the south side of the runway centerline. The test stripes were evaluated by 35 pilots and civil engineer personnel for approximately 15 months through visual comparison and measurement of the retroreflective intensities of the two lines.